The Marquette Interchange structures passed inspection with flying colors Monday, but WISN 12 News found that inspectors were not able to check for any potential problems in the ground where the bridges sit.

The inspections include the top side of the bridge and also the beams below, but they also go inside the bridge. Crews moved up into the underbelly of the structure.

They covered every inch of every bridge in the interchange, but they don't inspect the part of the bridge they can't see -- the part below ground. That's where the trouble occurred on Green Bay's Leo Frigo Bridge, with underground corrosion of a bridge piling.

REPAIR WORK IS UNDERWAY ON GREEN BAY'S DAMAGED LEO FRIGO BRIDGE. WHILE A MAJOR INSPECTION PROJECT WRAPS UP JUST A FEW HOURS AGO IN MILWAUKEE'S MARQUETTE INTERCHANGE. AND THERE IS A COMMON THREAD. 12 NEWS KENT WAINSCOTT IS BELOW THE INTERCHANGE, AND KENT, THERE'S ONE CRITICAL THING THE INSPECTORS WEREN'T ABLE TO CHECK. IT'S THE ONE PROBLEM THAT CAUSED THE RECENT BRIDGE TROUBLES IN GREEN BAY. THE STRUCTURES HERE PASSED INSPECTION WITH FLYING COLORS - BUT TODAY WE FOUND THAT INSPECTORS WERE NOT ABLE TO CHECK FOR ANY POTENTIAL PROBLEMS IN THE GROUND WHERE THE BRIDGES SIT. DRAPED OVER THE EDGE OF THE MARQUETTE INTERCHANGE - DOT BRIDGE INSPECTORS SCOUR THE STRUCTURE FOR SERIOUS PROBLEMS - BUT FIND NONE. BRIAN BLEISNER / CHIEF OPERATIONS ENG DOT - NO, AT THIS POINT, NO, THERE'S REALLY NO SIGNIFICANT ISSUES THAT WE'VE DETECTED. KENT - OF COURSE THE INSPECTIONS INCLUDE THE TOP SIDE OF THE BRIDGE AND ALSO THE BEAMS BELOW. BUT THEY ALSO GO INSIDE THE BRIDGE - CREWS MOVING UP INTO THE UNDERBELLY OF THE STRUCTURE. THE COVER EVERY INCH OF EVERY BRIDGE IN THE INTERCHANGE, BUT THEY DON'T INSPECT THE PART OF THE BRIDGE THEY CAN'T SEE - THE PART BELOW GROUND. THAT'S WHERE THE TROUBLE OCCURRED ON GREEN BAY'S LEO FRIGO BRIDGE, WITH UNDERGROUND CORROSION OF A BRIDGE PILING. BRIAN BLEISNER / CHIEF OPERATIONS ENG DOT - HOW DO YOU PREVENT SOMETHING LIKE THAT FROM HAPPENING AGAIN? - WELL, QUITE FRANKLY, IT'S NOT SOMETHING THAT WOULD TYPICALLY BE LOOKED FOR. THE CREWS DO WATCH FOR RED FLAGS THAT COULD BE A SIGN OF UNDERGOUND TROUBLE - LIKE UNUSUAL CRACKING OR SETTLEMENT OF THE BRIDGE - PROBLEMS OVERHEAD THAT MIGHT SIGNAL TROUBLE BELOW THE SURFACE. UNTIL NOW, THE INSPECTIONS HAVEN'T GONE THERE - BUT AFTER THE SITUATION IN GREEN BAY, BLEISNER SAYS THAT COULD CHANGE. BRIAN BLEISNER / CHIEF OPERATIONS ENG DOT - ANYTHING BELOW GROUND RIGHT NOW IS NOT PART OF OUR ROUTINE CHECK - IT MAY BE SOMETHING WE WOULD LOOK AT IN THE FUTURE BECAUSE OF THIS EXPERIENCE. THE D-O-T INSPECTS ALL BRIDGES EVERY TWO YEARS - BUT LARGER BRIDGES ON MAJOR ROADWAYS LIKE THIS GET A MORE IN-DEPTH INSPECTION EVERY FIVE YEARS. THAT ROUND OF WORK HERE IN THE MARQUETTE IS COMPLETE - THE D-O-T SAYS NEXT UP ARE THE BRIDGES IN THE MITCHELL INTERCHANGE. WORK STARTED TODAY TO REPAIR THE SAGGING LEO FRIO BRIDGE IN GREEN BAY. CREWS ARE TRYING TO STABILIZE THE SECTION THAT SANK ABOUT TWO FEET LAST MONTH. WHAT WE'RE GOING TO DO TODAY. DRILLING HOLES IN THE GROUND WHERE THE PILINGS ARE GOING TO GO. HOLD UP THE BRIDGE. THE D-O-T SAYS THEY'RE ALSO TAKING STEPS TO MAKE THE BRIDGE SITE IS SAFE FOR WORKERS. REPAIRS ARE EXPECTED TO WRAP UP NEXT MONTH AND WILL COST NEARLY 1-POINT-6